Lithium compounds are commonly used as initiators for anionic polymerizations. Such organolithium initiators can be employed in synthesizing a wide variety of rubbery polymers. For instance, organolithium initiators can be used to initiate the anionic polymerization of diolefin monomers, such as 1,3-butadiene and isoprene, into rubbery polymers. Vinyl aromatic monomers can, of course, also be copolymerized into such polymers. Some specific examples of rubbery polymers that can be synthesized using organolithium compounds as initiators include polybutadiene, polyisoprene, styrene-butadiene rubber (SBR), styrene-isoprene rubber, and styrene-isoprene-butadiene rubber (SIBR).
The organolithium compounds that can be used to initiate such anionic polymerizations can be either a specific organomonolithium compound or it can be a multifunctional type of initiator. In commercial applications monolithium compounds are normally used because they are available as pure compounds that are soluble in organic solvents. Multifunctional organolithium compounds are not necessarily specific compounds but rather represent reproducible compositions of regulable functionality. Many of such multifunctional organolithium compounds must be stored under refrigeration before being used.
U.S. Pat. No. 5,981,639 explains that multifunctional initiators used to initiate anionic polymerizations include those prepared by reacting an organomonolithium compounded with a multivinylphosphine or with a multivinylsilane, such a reaction preferably being conducted in an inert diluent such as a hydrocarbon or a mixture of a hydrocarbon and a polar organic compound. The reaction between the multivinylsilane or multivinylphosphine and the organomonolithium compound can result in a precipitate which can be solubilized if desired, by adding a solubilizing monomer such as a conjugated diene or monovinyl aromatic compound, after reaction of the primary components. Alternatively, the reaction can be conducted in the presence of a minor amount of the solubilizing monomer. The relative amounts of the organomonolithium compound and the multivinylsilane or the multivinylphosphine preferably should be in the range of about 0.33 to 4 moles of organomonolithium compound per mole of vinyl groups present in the multivinylsilane or multivinylphosphine employed.
U.S. Pat. No. 5,981,639 further notes such multifunctional initiators are commonly used as mixtures of compounds rather than as specific individual compounds. Other multifunctional polymerization initiators can be prepared by utilizing an organomonolithium compound, further together with a multivinylaromatic compound and either a conjugated diene or monovinylaromatic compound or both. These ingredients can be charged initially, usually in the presence of a hydrocarbon or a mixture of a hydrocarbon and a polar organic compound as a diluent. Alternatively, a multifunctional polymerization initiator can be prepared in a two-step process by reacting the organomonolithium compound with a conjugated diene or monovinyl aromatic compound additive and then adding the multivinyl aromatic compound. Any of the conjugated dienes or monovinyl aromatic compounds described can be employed. The ratio of conjugated diene or monovinyl aromatic compound additive employed preferably should be in the range of about 2 to 15 moles of polymerizable compound per mole of organolithium compound. The amount of multivinylaromatic compound employed preferably should be in the range of about 0.05 to 2 moles per mole of organomonolithium compound. Exemplary multivinyl aromatic compounds include 1,2-divinylbenzene, 1,3-divinylbenzene, 1,4-divinylbenzene, 1,2,4-trivinylbenzene, 1,3-divinylnaphthalene, 1,8-divinylnaphthalene, 1,3,5-trivinylnaphthalene, 2,4-divinylbiphenyl, 3,5,4xe2x80x2-trivinylbiphenyl, m-diisopropenyl benzene, p-diisopropenyl benzene, 1,3-divinyl-4,5,8-tributylnaphthalene and the like. Divinyl aromatic hydrocarbons containing up to 18 carbon atoms per molecule are preferred, particularly divinylbenzene as either the ortho, meta or para isomer and commercial divinylbenzene, which is a mixture of the three isomers, and other compounds, such as the ethylstyrenes, also is quite satisfactory.
U.S. Pat. No. 4,196,154 discloses organic liquid soluble multifunctional lithium containing initiators are prepared by reacting an organo lithium compound with an organic compound containing at least one group of the configuration 1,3-bis(1-phenylethenyl)benzene. U.S. Pat. No. 4,196,154 reports that such initiators can be prepared in the absence of polar solvents and are very desirable for the polymerization of dienes such as butadiene to a desirable 1,4 configuration.
This invention discloses a process for making dilithium initiators in high purity. This process can be conducted in the absence of amines which is desirable since amines can act as modifiers for anionic polymerizations. The dilithium compounds made are highly desirable because they are soluble in aromatic solvents and do not need to be stored under refrigeration.
The present invention more specifically discloses a process for synthesizing a dilithium initiator which comprises reacting diisopropenylbenzene with a tertiary alkyl lithium compound in an aromatic solvent at a temperature which is within the range of about 0xc2x0 C. to about 100xc2x0 C.
The present invention further discloses a process for synthesizing m-di-(1-methyl-3,3-dimethylbutyllithio)benzene which comprises reacting diisopropenylbenzene with tertiary-butyllithium in an aromatic solvent at a temperature which is within the range of about 0xc2x0 C. to about 100xc2x0 C.
The subject invention also discloses a process for synthesizing a functionalized lithium initiator which comprises the steps of (1) reacting diisopropenylbenzene with a tertiary alkyl lithium compound in an aromatic solvent at a temperature which is within the range of about 0xc2x0 C. to about 100xc2x0 C. to produce a dilithium initiator; and (2) reacting the dilithium initiator with a halide compound selected from the group consisting of (a) tin halides of the structural formula: 
(b) silicon halides of the structural formula: 
(c) amine halides of the structural formula: 
and (d) phosphorus halides of the structural foumula: 
wherein X represents a halogen atom, and wherein R1, R2, and R3 can be the same or different and represent alkyl groups, aryl groups, or alkoxy groups containing from 1 to about 10 carbon atoms.
The present invention also discloses a process for synthesizing a functionalized lithium initiator which comprises the steps of (1) reacting diisopropenylbenzene with a tertiary alkyl lithium compound in an aromatic solvent at a temperature which is within the range of about 0xc2x0 C. to about 100xc2x0 C. to produce a dilithium initiator; and (2) reacting the dilithium initiator with a compound having the structural formula: 
wherein X represents a neucleophile, and wherein R1, R2, and R3 can be the same or different and represent alkyl groups, aryl groups, or alkoxy groups containing from 1 to about 10 carbon atoms. The neucleophile will typically be selected from the group consisting of aldehydes, ketones, esters, halides, and acetals. Halides are typically preferred.
Dilithium initiators can be synthesized using the process of this invention by reacting a tertiary-alkyl lithium compound with m-diisopropenylbenzene in an aromatic solvent. The aromatic solvent will typically be an alkyl benzene. The alkyl group in the alkyl benzene will typically contain from 1 to 8 carbon atoms. It is preferred for the alkyl group in the alkyl benzene solvent to contain from 1 to about 4 carbon atoms. Some preferred aromatic solvents include toluene, ethyl benzene, and propyl benzene. Ethyl benzene is the most highly preferred aromatic solvent.
It is critical for a tertiary-alkyl lithium compound to be reacted with the m-diisopropenylbenzene. The tertiary-alkyl lithium compound will typically contain from 4 to about 8 carbon atoms. It is preferred for the tertiary-alkyl lithium compound to be tertiary-butyl lithium.
The reaction will typically be conducted at a temperature that is within the range of about 0xc2x0 C. to about 100xc2x0 C. It is normally preferred for the reaction between the tertiary-alkyl lithium and the m-diisopropenylbenzene to be carried out at a temperature that is within the range of about 10xc2x0 C. to about 70xc2x0 C. It is typically more preferred for the reaction temperature to be within the range of about 20xc2x0 C. to about 40xc2x0 C.
A functionalized lithium initiator can be prepared by reacting a dilithium initiator with a halide compound. Any dilithium initiator can be employed. However, dilithium initiators that are synthesized by reacting a tertiary-alkyl lithium compound with m-diisopropenylbenzene are highly preferred. The halide compound utilized will be selected from the group consisting of (a) tin halides of the structural formula: 
(b) silicon halides of the structural formula: 
(c) amine halides of the structural formula: 
(d) phosphorus halides of the structural formula: 
and (e) halides of the structural formula: 
wherein X represents a halogen atom, and wherein R1, R2, and R3 can be the same or different and represent alkyl groups, aryl groups, or alkoxy groups containing from 1 to about 10 carbon atoms. R1, R2, and R3 will typically be alkyl groups containing from 1 to about 4 carbon atoms or alkoxy groups containing from 1 to 4 carbon atoms. It is preferred for R1, R2, and R3 to be methyl groups (CH3-), ethyl groups (CH3-CH2-), methoxy groups (CH3-Oxe2x80x94), or ethoxy groups (CH3-CH2-Oxe2x80x94).
A compound of the structural formula: 
wherein X represents a neucleophile, and wherein R1, R2, and R3 can be the same or different and represent alkyl groups, aryl groups, or alkoxy groups containing from 1 to about 10 carbon atoms, can be reacted with the dilithium initiator in place of the halide compounds described above. In such compounds the neucleophile will typically be selected from the group consisting of aldehydes, ketones, esters, halides, and acetals. Halides are typically preferred neucleophiles.
The functionalization reaction will typically be carried out at a temperature that is within the range of about xe2x88x9280xc2x0 C. to about 150xc2x0 C. However, to enhance the probability of mono-functionlization, which reduces the probability of di-functionalization, the functionalization reaction will preferably be carried out at a reduced temperature. It is accordingly preferred for the functionalization reaction to be conducted at a temperature that is within the range of about xe2x88x9270xc2x0 C. to about 20xc2x0 C. It is normally more preferred for the functionalization reaction to be conducted at a temperature that is within the range of about xe2x88x9260xc2x0 C. to about 0xc2x0 C. It is also preferred for the halide compound to be added to a solution of the dilithium initiator (rather than adding the dilithium initiator to the halide compound).
The functionalized initiators made by utilizing the technique of this invention offer significant advantages when used to initiate the anionic polymerization of diene monomers, such as 1,3-butadiene or isoprene, into rubbery polymers. For instance, such functionalized initiators offer improved solubility in aliphatic solvents. More importantly, the rubbery polymers made with such functionalized initiators offer improved compatibility in rubber formulations that contain silica and/or carbon black. Such rubbery polymer can optionally be coupled with tin and/or silicon compounds. For instance, such rubbery polymers can coupled with tin tetrachloride or silicon tetrachloride.
This invention is illustrated by the following examples that are merely for the purpose of illustration and are not to be regarded as limiting the scope of the invention or the manner in which it can be practiced. Unless specifically indicated otherwise, parts and percentages are given by weight.